Efficiency analysis of 50 kWe SOFC systems fueled with biogas from waste water

Solid oxide fuel cell systems (SOFCs) are able to convert biogas from e.g. waste water plants highly efficiently into electricity and heat. An efficiency study of industrial sized solid oxide fuel cell systems installed at a waste water treatment plant is presented. The site consist of a biogas cleaning unit, two Convion C50 SOFC systems and a heat recovery section. The electric and total efficiencies of the systems are analyzed as a function of the electric net power output. The two systems achieved consistently high electric (50-55%) and total (80-90%) efficiencies in an electric net power output range between 25 kW and 55 kW. The study also shows that the high system efficiencies are independent of the CH4 content in the biogas. The results indicate that fuel cell systems are able to perform power modulation according to the power demand, while achieving constant high efficiencies. This is a clear benefit in comparison to micro turbines and combustion engines which are normally used for converting biogas into electricity and heat.